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Climate can exhibit abrupt shifts over large regions of the world. As the last glacial period was giving way to the current warm interglacial period, average temperatures in Greenland returned to glacial levels for more than 1,000 years. This unusual period, which is called the Younger Dryas, ended abruptly about 12,000 years ago. Evidence from an ice core drilled in Greenland indicates that temperatures there rose approximately 15°F (8°C) in less than a decade. No Audio.

During the last Ice Age, approximately one-third of all land was covered by glaciers. Glaciers reached as far south as New York City. This huge volume of ice reduced the amount of water in the oceans, which lowered sea level by several hundred feet. As a result, a land bridge joined Siberia to Alaska, making travel between the two continents possible. No audio.